Jesus said that a person must be born of both the water and the Spirit to enter the Kingdom of God (John 3:5). This refers to water baptism in the name of Jesus Christ and the gift of the Holy Spirit (Acts 1:5 and Acts 2:38). When the original Christians received the gift of the Spirit (born of the Spirit), they spoke in tongues (Acts 2:4; 10: 46; 19:6). Before Jesus ascended, He told His disciples that speaking in tongues would be a sign that follows those who believe and are baptized (Mark 16:17).
When a person receives the gift of the Holy Spirit, that personís spirit is united with the Spirit of God into what the Lord intends to be an eternal union. This is how a person receives everlasting life. So to answer your question, the gift of the Holy Spirit is a necessary element of New Testament salvation and those who receive this gift speak in tongues. I (David Huston) received this gift on November 13, 1981 and it was life-changing experience.
I am not suggesting by my comments that every person who speaks in tongues will automatically spend eternity with Jesus Christ. There is certainly more to salvation than speaking in tongues. For more on this subject, please read our articles in the Apostolic Free Library, Shelf 1, especially the article on Speaking in Tongues in Church.